Backup QB Johnson looks to impress

Colin Kaepernick had the most memorable play, Scott Tolzien had the most buzz-worthy performance and Josh Johnson had the most unglamorous assignment: mop-up duty.

Johnson was the fourth quarterback to enter the 49ers‘ preseason opener Friday, debuting with 8:04 left in the fourth quarter. When the 49ers signed Johnson, 26, in March, it was widely assumed the four-year veteran with five NFL starts would serve as Kaepernick’s primary competition for the backup job behind Alex Smith.

But Johnson wasn’t surprised when Tolzien preceded him during a 17-6 win over the Vikings. The order of appearance, he said, reflected the unofficial depth chart during training camp.

After Friday’s game, it appears that order won’t change in the near future.

Kaepernick, who had a 78-yard touchdown run, probably did enough to hold off the fast-charging Tolzien, whose 10-for-13 performance came on the heels of a head-turning training camp.

If the status quo remains, Johnson faces the possibility of not making the 53-man roster. He plans to make the most of his preseason opportunities, whenever they come. If his performance isn’t enough to make the cut in San Francisco, he could impress one of the NFL’s 31 other teams.

“All I really care about is the opportunity to go out and compete and show what I can do,” Johnson said. “Whatever happens is going to happen. It’s out of my control. … All I want to do is go out there, lead the offense, put good things on tape and let the chips fall where they fall. That’s the NFL.”

Johnson, who completed 2 of 4 passes for 30 yards on his two fourth-quarter drives, has more NFL experience than his competition – but Kaepernick and Tolzien have benefited from spending their rookie seasons learning the 49ers’ offense.

In contrast, Johnson is still, at times, thinking his way through plays instead of playing instinctively. During training camp, Johnson often has dashed from the pocket and taken off downfield on pass plays. It’s a nod to his scrambling ability – he has averaged 6.9 yards on 37 career rushes – but it’s also a reflection of his continuing education in San Francisco’s system.

Jim Harbaugh’s offense has evolved quite a bit since Johnson played for the 49ers’ head coach at the University of San Diego.

“I’m getting better every day,” Johnson said. “I’m making strides every day. I’m able to go out there and continue to play faster within the offense.”

Johnson’s immediate future might be murky, but he knows from experience how quickly fortunes – and depth charts – can change.

In 2009, his second NFL season, he was Tampa Bay’s No. 4 quarterback a week before the regular-season opener. A month later, however, after a trade and injuries, he was making his first of four consecutive starts.

“I feel like patience is the key because you never know,” Johnson said. “You never know what the future can hold. One thing in the NFL – and it’s easy to say, but it’s hard to do: Control what you can control and really keep that mind-set. I’ve seen a lot of crazy things happen.”